Since some fetuses are affected more than others, researchers advise no amount of alcohol can be deemed 'safe' for pregnant women

A recently published study by the University of Washington found that, due to genetic variance among fetuses, no level of alcohol consumption by pregnant women is safe.

A recently published study by the University of Washington found that, due to genetic variance among fetuses, no level of alcohol consumption by pregnant women is safe.

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A recently published study by the University of Washington found that, due to genetic variance among fetuses, no level of alcohol consumption by pregnant women is safe.

A recently published study by the University of Washington found that, due to genetic variance among fetuses, no level of alcohol consumption by pregnant women is safe.

Photo: Eakachai Leesin / EyeEm/Getty Images/EyeEm

UW Study: No amount of alcohol is safe for pregnant women due to genetic risk

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No two fetuses are affected by alcohol in the same way, thanks to genetics, and that could mean it's dangerous for pregnant women to consume even "light" amounts of alcohol -- despite some other research showing a small amount could be harmless.

A University of Washington study published last week examined 84 sets of siblings, including full siblings, half siblings, fraternal twins and identical twins, whose mothers had consumed alcohol while pregnant. Those with a more similar genetic profile, such as identical twins, which share 100 percent of each others' DNA, had similar "fetal alcohol outcomes," according to a UW Medicine news release. Siblings with greater genetic differences, such as half-siblings who share a mother, were impacted to a different degree.

The genetic connection to fetal alcohol syndrome means some fetuses are more vulnerable to alcohol than others, the study concluded, and fetuses can experience "vastly different outcomes."

"We don't fully understand all the ways fetal (and maternal) genetics influence alcohol's adverse impact on the developing fetus, although many studies are underway worldwide." Susan Astley Hemingway, lead author of the study and pediatrics professor at the University of Washington School of Medicine, said in the release. "We cannot clinically identify which fetus is more likely to be affected by alcohol exposure and which might be less vulnerable. There is not a test for that."

The study analyzed data that had been collected over 26 years. Researchers pulled the records of related pairs of siblings diagnosed with fetal alcohol syndrome. The study only examined children whose mothers reported drinking one glass of alcohol a day, and who were diagnosed with fetal alcohol syndrome at the same age, by the same team and using the same diagnostic system.

Taking all of those conditions into account, researchers then examined nine pairs of identical twins, 39 pairs of fraternal twins, 27 full sibling pairs and nine half-sibling pairs. The identical twins had no difference in their fetal alcohol outcomes, where as 44 percent of fraternal twins, 59 percent of full siblings and 78 percent of half-siblings experienced different outcomes.

That means, researchers concluded, even when exposed to alcohol at the same time and in the same amounts, genetics does play a role in how a fetus is impacted.

"What's fascinating is, with fraternal twins when they are not genetically identical, we see that, despite identical exposures, over half of them have different fetal alcohol outcomes," Astley Hemingway said in a video produced by UW Medicine. "Genetics is actually impacting how the alcohol affects the fetus. The same level of alcohol exposure that can be risky for one fetus can actually be of little risk or even more risk for the other fetus. This has huge public health implications."

Astley Hemingway's research comes as other studies have suggested that "light" drinking while pregnant is harmless. One Danish study published in 2014 concluded that women who drank one glass of wine or less per week during pregnancy had better behaved children.

In an op-ed published last spring in The Seattle Times, Astley Hemingway called such communications to pregnant women "disheartening."

"In reviewing 25 years of data from our FAS diagnostic clinic, it's clear to me that one drink per day can place a fetus at significant risk," she wrote. "One of every 14 children diagnosed with FAS at our clinic had a reported exposure of one drink per day."

Fetal alcohol syndrome is a birth defect caused by mothers drinking during pregnancy. Children affected typically have a growth deficiency, some facial anomalies and structural or functional brain damage. The Centers for Disease Control and Prevention (CDC) estimates three kids out of every 10,000 in the United States are affected.

"We are often asked if there is a safe amount to drink during pregnancy," Astley Hemingway said in a video produced by UW Medicine. "The answer is, since the same level of alcohol can do strikingly different levels of damage on two fetuses, that makes it difficult to identify a single level that will be safe for everyone. So it continues to be: the only safe amount is none at all."